Extract paths out of util (#13182)

This PR extracts the definition of the various Zed paths out of `util`
and into a new `paths` crate.

`util` is for generic utils, while these paths are Zed-specific. For
instance, `gpui` depends on `util`, and it shouldn't have knowledge of
these paths, since they are only used by Zed.

Release Notes:

- N/A

crates/assistant/src/context_store.rs

@@ -5,11 +5,12 @@ use fs::Fs;
 use futures::StreamExt;
 use fuzzy::StringMatchCandidate;
 use gpui::{AppContext, Model, ModelContext, Task};
+use paths::CONTEXTS_DIR;
 use regex::Regex;
 use serde::{Deserialize, Serialize};
 use std::{cmp::Reverse, ffi::OsStr, path::PathBuf, sync::Arc, time::Duration};
 use ui::Context;
-use util::{paths::CONTEXTS_DIR, ResultExt, TryFutureExt};
+use util::{ResultExt, TryFutureExt};
 
 #[derive(Serialize, Deserialize)]
 pub struct SavedMessage {